1. Field of the Invention
The present invention pertains to thermal printing media, and in particular, to thermal printing media having high mechanical strength.
2. Prior Art
Thermal printing media incorporating a heat sensitive substrate layer comprised chiefly of colorless or light colored thermally reactive leuco-type dyes and used for the recording of text and other types of visual information are conventionally known, for example, the material disclosed in Japanese Patent Application, First Publication Serial No. Sho-45-14035. Letters, numbers, patterns and the like can be recorded on this type of material by means of a thermal printer, using the thermal printing head therein for transfer of the image to the printing medium. This type of printing medium, therefore, offers a great number of advantages which are inherent to thermal printing methods. Namely, thermal printers tend to be relatively inexpensive and of compact design, operate cleanly and quietly, seldom require maintenance, and produce exceedingly legible printed images at a high output rate. Thermal printers are also widely available and are used for a great variety of printing applications including computer hard copy, cash registers and printing calculators, facsimile devices, and for many other devices which produce printed output. Additionally, use of thermally developing printing media eliminates the need for additional fixing or developing processes.
One application for which the above described type of heat sensitive media has enjoyed rapidly expanding popularity in recent years is for labels or tags. For example, such tags indicate the destination of the traveler to whom the luggage belongs and are attached to stowed luggage in commercial aircraft. These tags may be exposed to extreme temperature conditions in the luggage compartment of an aircraft in flight, and furthermore, are subject considerable physical abuse in the course of baggage handling and transport. Thus, these tags must be able to withstand considerable shearing forces, as well as abrasion to surfaces thereof if they are to survive intact with the printed information clearly legible so as to serve their ultimate purpose of indicating the destination of the luggage.
One method which has been conventionally applied in order to improve the durability of such luggage tags is to apply a thermal printing paper having a protective layer over a synthetic resin film, thereby enhancing the mechanical strength thereof. Application of the synthetic resin film, however, necessitates additional steps in the manufacture of the labels and tags, thereby increasing their cost. Furthermore, with application of heat during printing, adhesives used to attach the synthetic resin film to the thermal printing paper tend to fog the thermal paper and may exude from the sides of the labels and tags, leading to maintenance problems if the exuded adhesive accumulates on the thermal printing head or other components of the printer.
Additionally, paper supported thermal printing media have certain limitations in the achievable resolution. For this reason, such media may be unsuitable for printing of high precision bar codes which been implemented in recent years.